This invention relates to waveguide apparatus and in particular, but not exclusively, to apparatus comprising a waveguide consisting of two or more sections.
With the advent of modern transceiver/receiver technology, often operating at millimeter wavelengths, it is sometimes necessary to use what is commonly referred to as E-plane technology.
E-plane technology refers to the technique of mounting devices in the E-plane or electric field plane of the dominant mode of the waveguide. This plane usually extends along the waveguide perpendicular to the broadwall of the waveguide at the position where the radio frequency current is a minimum, normally in the plane bisecting the broadwall.
In a known configuration, when using the above technology, components are mounted on a dielectric substrate as shown in FIG. 1 of the accompanying drawings, where the dielectric 1 is held in position by being sandwiched between the mating surfaces 2 of sections 3 and 4 which comprise the waveguide.
Unfortunately, by inserting the substrate between the sections of the waveguide there is a discontinuity of the metallic inner wall of the waveguide at the dielectric. This results in power losses from the guide through the substrate layer and is detrimental to the performance of the waveguide.
In order to reduce losses through the substrate layer the apparatus shown in FIG. 2 of the accompanying drawings has been proposed. The dielectric substrate 5, normally in the form of a PCB, is located in detents 6 in the waveguide 7. As the substrate does not extend across the whole width of the waveguide walls there is thus a continuous inner metallic wall and therefore no escape path for the signal being propagated along the waveguide. However, this technique requires precise machining of the guide and substrate and leads to problems in connecting components carried by the substrate to apparatus outside the waveguide.
An alternative apparatus is shown in FIG. 3. The dielectric substrate 8 may have components mounted on it, prior to assembly, which can be connected via conductors carried by the substrate to the external wall 9. Construction tolerances are not so critical, as the substrate is simply sandwiched between the sections 10 and 11 of the waveguide, and can therefore be produced more cheaply than the apparatus shown in FIG. 2. To reduce the losses from the waveguide cavity 12 via the dielectric substrate 8, the substrate extends into secondary cavities 13 and 14 on either side of the waveguide. These behave as radio frequency chokes limiting power losses from the central cavity 12. However, there may still be an appreciable power loss from the waveguide and the bulk of the structure is considerably increased.
British patent application GB No. 2 207 009, published Jan. 18th, 1989, describes apparatus as shown in FIGS. 4A, 4B and 4C, for reducing the above-mentioned power losses without increasing the bulk of the waveguide.
Slots 15 are incorporated within the dielectric 17 separated by gaps d as shown in FIG. 4A. These slots 15 are through-plated so as to have a conductive layer 16 on their inner surfaces. When the substrate is assembled between two sections of the waveguide 18 and 19 as shown in FIG. 4B, and FIG. 4C. (which is a transverse cross-sectional view of the waveguide), the inner conductive surfaces 16 of the slots 15 bridge the gap between the sections 18 and 19. This effectively continues the metallic wall of the waveguide across the dielectric region 17, except in the regions of the gaps between adjacent slots, d, which still permit some power loss from the guide.
The object of the present invention is to control further these power losses.